Dish assembly

ABSTRACT

A dish assembly is disclosed which has a central hub, an outer rim member, and a plurality of concentric arcuate structural members comprising at least an inner and an outer arcuate structural members extending from the central hub to the outer rim member, each of the arcuate structural members having an upper channel member, a lower channel member, an inner arcuate surface and an outer arcuate surface which cooperate to constitute a box section configuration and wherein said each upper and lower channel member comprises a channel base and a pair of channel flanges, and the inner and outer arcuate surfaces of each of the arcuate structural members are abutted such that a gravitational or wind load is transferred from the outer arcuate structural member to the adjoining inner arcuate structural member via a fin disposed on the inner arcuate surface of each of the arcuate structural members.

This application is a 371 of PCT/AU03/00964 Jul. 30, 2003.

TECHNICAL FIELD

This invention relates to a dish assembly.

As used herein the expression dish assembly refers to any dislikestructure the surface of which is curved such as by way of example, in aparaboloid or conic surface.

The invention has particular but not exclusive application to dishassemblies which collect solar radiation and in this specification theinvention will be described by reference to its application to solarcollectors. However it will be appreciated that the dish assembly of thepresent invention may be utilised in other applications utilising dishassemblies such as for example, dish antennas for radio telescopes andsatellite or other wireless communication.

BACKGROUND OF INVENTION

Dish assemblies for collecting and concentrating solar radiation areknown which concentrate direct solar radiation in excess of 1000 timesby the reflection of incoming direct or beam radiation. These systemsautomatically track the sun with a total error of less than 0.1 sundiameters and provide a reduced aerodynamic profile to survive in highwinds. They maintain the position of a receiver or a receiver-converterto the focus of the concentrated radiation to better than 0.1 sundiameters, and attempt to achieve minimum costs for manufacture,installation and maintenance. The known assemblies have aperture orcollecting areas usually between 100 and 150 sq. metres although a fewassemblies exceed 250 sq. metres.

SUMMARY OF INVENTION

The present invention alms to provide an alternative to known dishassemblies.

This invention in one aspect resides broadly in a dish assemblyincluding:—

a central hub;

an outer rim member, and

a plurality of concentric arcuate structural members extending from thecentral hub to the outer rim member;

the arcuate structural members being of box-section configuration andabutting along their inner and outer arcuate surfaces such that load canbe transferred from an outer arcuate structural member to an innerarcuate structural member.

As used herein the expression “box-section configuration” refers to astructural member having at least three sides of which all or all exceptone, are wall members, the one excepted side if not a wall member beingbraced to maintain the box-section configuration when the arcuatestructural member is under load.

As used herein the expression wall member is to be given a broad meaningand refers to any substantially planar substantially rigid sheet-likematerial. The expression covers material which is not necessarilycontinuous such as sheet metal having cut-out portions.

The arcuate structural members may constitute annular rings. However itis preferred that the arcuate structural members constitutes arcs offinite length and that the dish assembly includes a plurality of radialsupport arms extending from the central hub to the outer rim member andadapted to support the ends of the arcuate structural members.

It is also preferred that the arcuate structural members have an upperand lower channel member which cooperate to constitute the box-sectionconfiguration.

It is also preferred that the upper and lower channel members are formedfrom substantially rectangular metal sheeting.

It is also preferred that the gauge of the metal sheeting from which thearcuate structural members are made is greater in an inner arcuatestructural member than in an outer arcuate structural member.

It is also preferred that the upper and lower channel members have atransverse rib formed within the channel across the channel base betweenthe channel flanges, the rib being formed from the base.

It is also preferred that the rib is formed by folding inwardly aportion of the base, the fold being deeper at one flange than the othersuch that the rib is correspondingly deeper at one flange than theother, whereby the rib constitutes a cantilever and whereby the edges ofthe substantially rectangular sheet becomes angled about the rib tothereby form the arc in the arcuate member.

It is also preferred that the flanges of the upper and lower channelmembers have outwardly and inwardly directed returns at the respectivetoes thereof, such that when the upper and lower channel memberscooperate to constitute the arcuate structural member of box-sectionconfiguration, the returns constitute cooperating keys and recessesrespectively of adjoining concentric arcuate structural members wherebyload can be transferred from an outer arcuate structural member to anadjoining inner arcuate structural member.

It is also preferred that the dish assembly includes a plurality ofmirrors affixed to the bases of the upper channel members whereby thedish assembly constitutes a solar collector.

It is also preferred that the mirrors are substantially square withsides substantially the width of the arcuate structural members.

It is also preferred that the dish assembly includes a dish supportmember supportable on a foundation and receivable within an opening inthe hub member and adapted to cooperate therewith to elevate the dishassembly with respect to the foundation.

In another aspect this invention resides broadly in a dish assemblyincluding:—

a central hub having a central opening therein, and

and a dish support member supportable on a foundation and receivablewithin the central opening of the hub member and adapted to cooperatewith the hub member whereby the dish assembly is elevated with respectto the foundation.

It is preferred that the dish support member is an arcuate beam alongwhich the hub member travels whereby the dish can be positioned betweena first position where it rests substantially on the ground with itsaxis substantially vertical and a second position where it is supportedon the dish support member with its axis substantially horizontal.

It is also preferred that the dish support member is mounted on arotatable platform such that the azimuthal positioning of the dish canbe varied.

In another aspect this invention resides broadly in a method of erectinga dish assembly at a remote location, the dish assembly having a centralhub and an outer rim member, the method including:—

transporting to the remote location a plurality of flat stackedsubstantially rectangular metal sheets or nested sections formedtherefrom;

at the remote location forming a plurality of arcuate structural membersof box-section configuration from the substantially rectangular metalsheets or from the sections formed therefrom, and

positioning the plurality of arcuate structural members to extendconcentrically from the central hub to the outer rim member, the arcuatestructural members abutting along their inner and outer arcuate surfacessuch that load can be transferred from an outer arcuate structuralmember to an adjoining inner arcuate structural member.

It is preferred that the method also includes:—

positioning a plurality of radial support arms extending from thecentral hub to the outer rim member, and

supporting the arcuate structural members on the radial support arms.

It is also preferred that the method includes:—

forming the substantially rectangular metal sheets or the sectionsformed therefrom into upper and lower channel members, and

joining the upper and lower channel members to form the arcuatestructural members.

It is also preferred that the method includes forming within the channeland from the channel base a transverse rib across the channel basebetween the channel flanges.

It is also preferred that the method includes folding inwardly a portionof the base, the fold being deeper at one flange than the other suchthat the rib formed thereby is correspondingly deeper at one flange thanthe other, whereby the rib constitutes a cantilever and whereby theedges of the substantially rectangular sheet becomes angled about therib to thereby form the arc in the arcuate member.

It is also preferred that the method includes:—

mounting a dish support member on a foundation, and

supporting the dish assembly on the dish support member via an openingin the hub member which is adapted to cooperate with the dish supportmember to elevate the dish assembly with respect to the foundation.

In another aspect this invention resides broadly in a method ofelevating a dish assembly above a foundation, the method including:—

providing an opening in a central portion of the dish assembly;

mounting a dish support member on the foundation;

supporting the dish assembly on the dish support member within theopening, and

causing the dish assembly to travel along the dish support member.

DESCRIPTION OF DRAWINGS

In order that this invention may be more easily understood and put intopractical effect, reference will now be made to the accompanyingdrawings which illustrate a preferred embodiment of the invention,wherein:—

FIG. 1 is a side elevation of the dish assembly of the present inventionshown at an elevation of 60 degrees;

FIG. 2 is a front-on view of the dish assembly shown fully elevated andillustrating the concentric bands of mirrors positioned on theconcentric arcuate structural members and showing the hub, radialsupports and outer rim;

FIG. 3 is an enlargement of a portion of FIG. 2 showing the mirrors ingreater detail;

FIG. 4 is a sectional elevation of the dish assembly shown fullyelevated;

FIG. 5 is a side view showing two dish assemblies in a stowed positionadjacent the dish foundation;

FIG. 6 is plan view showing the dish platform and illustrating in lightrelief the fully elevated and fully stowed dish positions;

FIG. 7 is a perspective view showing an arcuate structural member;

FIG. 8 is a perspective view of the upper and lower channel membersrespectively prior to the formation of ribs to bend the channels to anarcuate form;

FIGS. 9A AND 9B are perspective views of the upper and lower channelmembers respectively after formation of ribs and which when assembledform the box-sectioned configuration of FIG. 7;

FIG. 10 is a perspective view illustrating the operation of a tool toform the ribs, and

FIGS. 11 and 12 are orthographic projections which respectivelyillustrate a substantially rectangular metal sheet before and after theformation of the ribs;

FIGS. 13A-13D are side views illustrating the operation by which theribs are formed. FIGS. 13A and 13C show the operation of the tool whichforms the ribs thereby changing the cross-sectional profile of the upperor lower channel members from that seen in FIG. 13B, which correspondsto the tool being in the position shown in FIG. 13A, to that seen inFIG. 13D which corresponds to the tool being in the position shown inFIG. 13C;

FIG. 14 illustrates the derivation of the bend angle resulting from thechannel and rib-forming operation;

FIG. 15 illustrates a sub-faceting process for enhancing theconcentration of the solar collection;

FIG. 16 is an annotated illustration of the dual ram arrangement of theazimuth drive for 540 degrees rotation;

FIG. 17 is an annotated illustration of another arrangement of the dualram of the azimuth drive;

FIG. 18 is an annotated illustration of the dual ram arrangement forelevating the dish, and

FIG. 19 is an annotated illustration of the dual ram arrangement forstowing the dish.

DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION

As can be seen throughout the drawings, in a preferred embodiment thepresent invention provides a dish assembly 10 having a central hub 11,an outer rim member 12, and a plurality of concentric arcuate structuralmembers 13 extending from central hub 11 to outer rim member 12 (seeFIG. 1). The arcuate structural members 13 are of box-sectionconfiguration (see FIG. 7) and abut along their inner and outer arcuatesurfaces 14,15 respectively such that load can be transferred from anouter arcuate structural member to an inner arcuate structural member.

The arcuate structural members 13 constitute arcs of finite length anddish assembly 10 has a plurality of radial support arms 36 (see FIG. 2)extending from central hub 11 to outer rim member 12. The radial supportarms 36 support the ends 16,17 (see FIG. 7) of arcuate structuralmembers 13.

Arcuate structural members 13 have an upper and lower channel member18,19 (see FIGS. 7 to 9) which cooperate to provide the box-sectionconfiguration. As seen in FIGS. 10 to 13, upper and lower channelmembers 18,19 are formed from substantially rectangular metal sheeting20. Upper and lower channel members 18,19 have transverse ribs 21 formedwithin the channel across the channel base 22 between the channelflanges 23,24.

The ribs 21 are formed from the material of channel base 22 (see FIGS.7, 8, 9A, 9B, 10 and 12) by folding inwardly a portion of channel base22 with the fold 25 being deeper at one flange 23 than at the otherflange 24 such that rib 21 is correspondingly deeper at one flange 23than the other 24 (see FIGS. 9A and 9B). Each rib 21 thus constitutes acantilever. Furthermore because of the sacrificial formation of the ribs21 from the base material 22 the edges of the substantially rectangularsheet 20 is angled about the rib 21 to thereby form the arc in thearcuate member 13.

Flanges 23,24 of upper and lower channel members 18,19 have outwardlyand inwardly directed returns 27,28 at the respective toes of theflanges (see FIGS. 7, 8 9A and 9B). Accordingly, when upper and lowerchannel members 18,19 cooperate to constitute the arcuate structuralmember 13 having box-section configuration, the returns 27,28 constitutecooperating keys 29 and recesses 30 (see FIG. 7) respectively ofadjoining concentric arcuate structural members 13 whereby load can betransferred from an outer arcuate structural member to an adjoininginner arcuate structural member.

As can be seen in FIG. 3, the dish assembly has a plurality of mirrors31 affixed to the channel bases 22 of the upper channel members 18whereby the dish assembly constitutes a solar collector. Minors 31 aresubstantially square with sides substantially the width of the arcuatestructural members.

To allow the dish assembly to be elevated, a dish support member 32 ismounted on rotatable platform 35 which is supported on a foundation 33(see FIG. 1). Dish support member 32 is received through an opening inhub 11 and the two cooperate to elevate the dish assembly 10 withrespect to foundation 33.

It will also be appreciated that in another preferred embodiment thepresent invention constitutes a dish assembly 10 having a central hub 11with a central opening therein, and a dish support member 32 which issupported on a foundation 33 and is received within the central openingof hub member 11 and cooperates with hub member 11 to elevate dishassembly 10 with respect to foundation 33. Dish support member 32 is anarcuate beam along which the hub member 11 travels whereby the dish 10can be positioned at intermediate locations (as seen in FIG. 1) betweena first position (as seen in FIG. 5) where it rests substantially on theground with its axis substantially vertical and a second position (asseen in FIG. 4) where it is supported on the dish support member 32 withits axis substantially horizontal.

Dish support member 32 is mounted on a rotatable platform 35 such thatthe azimuth positioning of the dish can be varied.

In general terms it can be seen that the dish assembly of the presentinvention (hereinafter “the dish”) is a large circular shell shapedstructure, about 25 metres in diameter, formed by a series of nestedconcentric hollow box sectioned polygonal rings made up of arcuatesegments 13 fitted within an outer ring 12. The polygonal rings aremanufactured from sheet metal and preferably the thickness of the metaldecreases with increasing diameter. The polygonal rings are divided intoappropriate sectors to facilitate handling during manufacture andassembly and are joined at bracing plates (the radial supports 36)positioned on radii which connect sectors of the same polygonal ring andadjacent rings together.

The inner and outer sides 14,15 of each of the box sectioned nestedpolygonal rings are parallel to the common dish axis and aremanufactured to include recesses 30 and projections 29 alongcircumferential lines through their centres. The top and bottom facesare symmetrical about radii to, and constructed to be angled to planesorthogonal to, the common axis. The top faces of the nested box sectionsform facets that approximate the concave surface of a paraboloid.Pressed shallow diagonal grooves 37 stiffen the bottom and top faces inconventional manner. (See FIG. 7 where one such set of grooves is shownfor exemplary purposes). Where required, the bottom faces haveapertures, or portions are cut out of the bottom face, for access tofixing fasteners or to facilitate fixing processes. Flat mirrored glasssheets 31 are bonded to the angled top faces. The top faces of the boxsection are designed to provide the appropriate angles for reflectingincoming-radiation that is parallel to the common axis, to the focus forconcentrating the radiation.

As can best be seen in FIGS. 13 and 14, the angulation of the boxsections 13 to the dish axis is achieved by the angle at which theflanges 23,24 are bent to the respective faces 22. Flanges 23, 24 areformed by folding the rectangular metal sheeting 20, and are angled tothe channel member base 22. The angle through which the innermost flange23 is folded is herein termed the bend angle. The outer flange 24 isfolded parallel to flange 23. In the preferred arrangement, the bendangle changes from approximately 90 degrees at the hub to approximately113 degrees at the outer rim member 12, and is unique for of the arcuatestructural members 13.

The derivation of the bend angle is derived in the manner explained withreference to the geometry of FIG. 14 where the line AS is the axis ofthe dish through the focus, F, and is presented as a vertical line. Thepoints S and F are fixed, the co ordinates of S dependent on theposition relative to the hub of the inner flange of the arcuatestructural member being considered and the co ordinates of F dependenton the preferred focusing properties of the dish.

When AB is aligned to a radiation source, the vertical line through Prepresents direct beam radiation to be reflected at P to intercept AB atF.

T, P and S are co-linear and P is the midpoint between T and S. A normalto ST through P intercepts AB at B. The distance between S and T isconstant being the width of the base, 22, of the channel member, 20. Aline through T, P and S intercepts AB at A.

The bend angle is derived by rotating ST about S, changing the directionof PB and PA and their intercepts on AB, until the length FA equals thelength FB. The angle between ST and a horizontal intercept on ST isrepresented by the symbol gamma. The bend angle is 90 degrees plusgamma.

The top face may be deformed during the manufacture to produce a numberof flats or facets appropriately angled relative to the single facetangle, such than when smaller flat mirrored glass sheets are attached,the concentration is increased. This is illustrated in FIG. 15.

The outer ring 12, the mirrored polygonal rings 13 and bracing plates 36are assembled around the hollow cylindrical hub 11 and braced by rodspokes 48. The rings and hub have the same axis and one end of the hubis positioned approximately 1 metre from, and on the non-dish side ofthe plane of the outer ring intercept on the axis.

The hub is about 5 metres in length and 1 metre diameter, and isattached on its outside surface, about 1.5 metres from its end on theconvex side of the dish, to one end of a radial strut 39, which may beregarded as constituting a torque tube. This tube is about 12 metreslong and is sufficiently strong to adequately resist bending andtwisting. The diameter of the hub and the axis of the torque tube are inalignment at their point of connection.

The torque tube is attached at its other end to the centre of a bearingtube, which is a cylindrical beam about 18 metres long. This forms a teewhich is braced by struts connected each side to the approximate centreof the torque tube and the ends of the bearing tube. The axis of thetorque tube is at right angles to the axis of the bearing tube andaligned with the bearing tube diameter.

The receiver 40 is configured to be rigidly suspended about the focus tointercept the concentrated radiation. The preferred support for thereceiver is a central column attached to the hub, stabilized by guys 41to the outer ring and aligned with the dish axis.

The dish is connected to a base comprising a frame of structural “I”beams approximately 0.6 metres deep in the form of a cross in thehorizontal plane. The major arm 42 of the cross is approximately 18metres long and the minor arm 43 is approximately 15 metres long (seeFIG. 6) and they are connected approximately 4 metres from one end ofthe major arm. Structural “I” beams 44 are approximately 0.25 metresdeep and 3 metres long and constitute small arms which are attached oneach side and parallel to the minor arm. Bracing rods are attachedconnecting adjacent ends of the cross and connections between midpointsof the adjacent arms of the cross. The major arm is modified to increaseits torsional stiffness by attaching side plates to form parallel boxsections in the length between the minor arm intersection and the end ofthe small arms. Horizontal axis bearings are attached at the ends andthe centre of the minor arm.

The base carries has wheeled bogey assemblies 45 at its extremities andalso has an azimuth pivot bearing 46 and vertical shaft about half wayalong its major arm. The bogies carry vertical down loads to thefoundations and are aligned to follow a circular path and the pivotbearing carries horizontal and up and down vertical loads.

The elevation drive beam 32 is an “I” section curved beam, and isconnected to one end of a vertical strut 47 forming a support post at anend of the curved beam. The other end of the support post is connectedto the end of the major arm 42 of the base, nearer the minor arm 43. Theremaining end of the elevation drive beam is connected at the other endof the major arm so that the plane of curvature is in the vertical planeabove the major arm 42 of the base. The “I” section is approximately 0.8metres deep in the plane of curvature, the radius of curvature for theneutral axis in the vertical plane is about 12 metres and the arc lengthis approximately a quarter of a circle. The upper end of the supportpost is braced by nods fixed to the ends of the small arms.

The reinforced concrete foundations 33 are of sufficient strength tocarry the gravitational and aerodynamic loads, and comprise a horizontalring approximately 18 metres in diameter forming a flat circular trackfor the bogey wheels. The wheels are tired with a high strength polymersuited to the transfer of the vertical down loads to the concrete.Radially directed structural reinforced concrete crossbeams connect thecentre of the ring to the circular track foundation and, where theyintersect, provide a mounting for the azimuth pivot bearing verticalshaft.

The three major elements ie dish, base and foundations are assembled toform a system that facilitates the rotation of the dish about verticaland horizontal axes. The dish is connected to the base by 3 sets ofbearings and shafts in the bearing tube that are supported from theminor arm of the base on raised plumber blocks. The height of the blocksabove the minor arm is sufficiently greater than the radius of thebearing tube to allow the bearing tube to rotate. The bearing tube ismanufactured with an opening in the tube wall at the centre to allow theraised plumber block to align with the bearing tube axis. The angulardisplacement of approximately 90 degrees about the horizontal axis, isachieved by the actuation of a drive mechanism applying forces betweenthe elevation drive beam attached to the base and the hub of the dish.

The angular displacement of the base and dish combination of +/−135degrees about the vertical axis is achieved by the actuation of a drivemechanism applying forces between the base and the foundations. Thepreferred drive is by one of a pair of double acting hydraulic cylindersor rams with appropriate pumps, control valves and interconnections,applying force between mechanical connections on the fixed and movingelement. An automated control process changes the drive betweencylinders when the limit of extension or retraction is reached.

To rotate the base and dish supported on the wheeled bogies about thevertical axis, the two rams are attached to suitable pivots on thefacing sides of the crossbeams and within one of the quadrants formed bythe crossbeams. One ram connects to a drive pin on the base via a camoperated coupling in a configuration such that upon extension orretraction it applies a torque to the base, about the vertical axis.

The second of the two rams, when not in use, is maintained in its fullyextended position and is connected to the drive pin via a cam operatedcoupling when the first ram approaches its full extension. The couplingis configured such that at least one ram is always connected and thefirst ram is disconnected as the second ram retracts. The transitionoccurs when both rams are at near full extension and takes place overapproximately 15 degrees of rotation. The second ram, by extending orretracting, applies a torque to the base about the vertical axis.

The dish and base combination will rotate when the torque from eitherram is sufficient to exceed the resisting torque generated by bearingfriction, inertia and wind loads. Each ram is configured to havesufficient extension to rotate the dish and base combination through 135degrees and transition between the rams takes place when the horizontalaxis of the dish is orthogonal to the vertical north/south plane. Ifrequired, at full rotation, the driving ram can be disconnected by amanual operation and the dish rotated a further 45 degrees under anexternal drive.

The double ram arrangement is suited to regions in both hemispheresbeyond the tropics where the rotation is by one pole. In tropicalregions rotation about the vertical axis is required via both poles andthe preferred option is for a single double acting hydraulic cylinder todrive a rack and spur gear combination at the hub, extending the rangeto plus and minus 270 degrees.

The hydraulic ram in this configuration (see FIG. 16), has anarrangement whereby the rod is fixed to the foundation and the cylinder,with rack attached, moves as fluid is displaced from one side of thepiston to the other. The valve and pump arrangement is designed tominimise fluid inventory.

To rotate the dish supported on the bearing tube about the horizontalaxis, the two rams are attached to suitable pivots within the hub. Therams operate alternatively, each four times, connecting anddisconnecting from the elevation drive beam via hydraulic actuated camsor locks. The cams are configured such that at least one ram is alwaysconnected.

When the rams are identical, the volume displaced while extending oneram is identical to the volume required for retraction of the other ramat the same rate. The control system and valves compensate for smalldifferences.

At the completion of a full extension or retraction, the unconnected ramis aligned with another connecting cam and is connected by a mechanismdriven by the force of the connecting ram in the form of a small doubleacting hydraulic cylinder.

For illustrative purposes, annotated drawings as per FIGS. 16-19describe the operation of the double acting ram in the variousconfiguration of azimuth and elevational positioning of the dish.

Under the control of an electronic system, the driving rams on both axesextend or retract and appropriate cams engage or disengage, to rotatethe dish and align the dish axis with the required direction.Preferably, the driving only takes place when an angular differencebetween the required direction and the dish axis is unacceptable. In asun-tracking mode the acceptable difference is approximately 0.1 degreeand the changeover of the ram drive within a pair is achieved beforethis difference is exceeded.

The tracking process can proceed through its full angular range, 90degrees in elevation and +/−135 degrees in azimuth, for winds up to thedesign tracking-wind velocity. For wind velocities above the trackingvelocity, the dish is stowed in its survival position, zero elevation,concave side up.

It will be appreciated that the dish is designed such that the mountingpoints for the mirrors are determined by the accuracy of the position oftheir polygonal ring. The process of nesting and fastening ringstogether, the inclusion of bracing plates and their bracing by spokes,the structural properties of a box section and the hoop strength of aring, combine to maintain these mounting points in space to the requiredaccuracy of the optical system. The mirror mounting faces are positionedto an approximate paraboloid and no adjustment is allowed for in thedesign.

All mirror pieces are squares of the same size. The mirror sizedetermines the concentration with the smaller the square, the higher theconcentration. For high concentration, sub-facets are pressed into themain face formed as part of the polygonal surface. The nested polygonalrings are manufactured on site from galvanized sheet steel, are bracedby spokes to a hub, and form a quasi-continuous surface, approximatingthe shape of a paraboloid to carry mirrors. The shape is approximatebecause of the optics associated with flat facets requiresdiscontinuities (semi fresnel) along a radial line on the surface. Forhigher concentration ratios, some degree of concavity may be produced bysub-faceting the polygonal face and subdividing the mirror into smalleryet still square pieces. The preferred concentration ratio for thisdesign with flat mirrors is 1000:1 (as seen in FIG. 15). Ratios achievedwhile maintaining square glass mirrors, each of the same size but onequarter or one ninth of the original, are stepped, 1000:1, 4000:1 and9000:1, e.g. panel as a flat, sub-faceted 2×2, sub-faceted 3×3.

The dish has a horizontal axis pivot tangential to the rim and in theplane of the dish centre normal to the dish axis and rotates inelevation about the horizontal axis by the application of a force at itscentre and relies on the torque tube connection to the bearing tube toprovide the counter to transverse out of balance wind forces.

The transfer of the gravitational and wind loads in the dish is in partvia each polygonal ring sector terminating at the radial bracing platesthat are rod braced to the hub by rods 48. The flanged box sectionintercept when attached to the bracing plate, reinforces the plateagainst local buckling. Additionally, each sector transfers to the nexttowards the centre, via the fin 29 on the inner polygonal vertical face14. This fin 29 engages in the matching cavity 30 or groove on the outerpolygonal vertical face 15 of the next ring.

The polygonal forming process produces internal tapered beams or ribs21, top and bottom, in the box section and produces the vertical beams49 on the inner surface 14 connected to the fin 29. When the fin 29engages the groove 30 and is fastened to the groove, that same verticalbeam 49 stabilises the outer face 15 that carries the groove 30 againstbuckling. The final coupling to the hub 11 is via a fabricated groove(not shown) comprising the space between two closely spaced rings towhich the innermost polygonal section fin engages and is fastened. Thedesign takes into account the summing effect of loads on all previousrings as the centre hub is approached and the added strength is providedby increased metal thickness for the inner rings. The depth of theinternal beams increases with decrease in diameter of the rings and soincreases the stiffness with increasing load.

The dish is assembled on-site on its base with the only prefabricatedfactory made components being the hub, torque tube, bearing tube andouter ring. The heaviest of these components is the torque tube 39 at1.5 tonnes and can be placed in position with a medium size forklift.The bracing plates 36 are 150 KG, 6 mm thick, galvanized, sheet steelribs that bolt to cleats on the hub 11 and brace to the top and bottomof the hub with solid steel rod spokes. The spokes are threaded at oneend for tensioning. Apart from the attachment points of the spokes tothe top of the hub all elements in the assembly are less than 3 metresabove the base. This is a major advantage compared to the 7 to 10 metresof the comparative systems.

The polygonal box sections are formed on site from flat or coiled steelsheet that preferably has been prepared in a factory by prepunching andfor flat sheet, preforming one edge by bending a small reference upturnof approximately 60 mm. With only one edge upturned flat sheets can bestacked compactly one on another for efficient transport if in flatsheet form, it is cut to length to match the range of polygonal sectorsrequired. The prepunching produces appropriate cutouts that allow beamsto form at the same time on adjacent but angled surfaces and to providefor access for the fastening devices that insert the fasteners to joinnested rings.

A specifically designed bending mechanism for forming an upper (18) andlower (19) part of the polygonal ring is illustrated in FIGS. 13A and13C. The two parts or channels 18,19 which when fastened together formthe box section 13, have flanged and punched ends formed as part of theprocess. The fastening together is preferably by double sided adhesivetape and is of sufficient strength to allow the sector to be handled,have the mirrored glass attached and transferred to the dish forattachment to the previously mounted ring and bracing plates. The finalfastening of the two pieces is incorporated in the fastening of adjacentnested rings, where fins in grooves are joined together at regularintervals in a semiautomatic process.

Turning to the illustrations of FIGS. 13A to 13D, it will be seen thattool 50 forms the ribs 21 and 49 thereby changing the cross-sectionalprofile of the upper or lower channel members from that seen in FIG.13B, which corresponds to tool 50 being in the position shown in FIG.13A to that seen in FIG. 13D which corresponds to tool 50 being in theposition shown in FIG. 13C Tool 50 comprises a force applicator 51 whichprovides a force at an angle determined by the setting of angle adjuster52 which is set to half the bend angle. The force is applied at thepredetermined angle to a pair of coupled rollers 53,54 whichrespectively apply force to a first male die 55 and a second male die56. Die 53 is pivoted at an upper point and engages with a female die 57at an increasing depth away from the pivot point. Die 55 is adapted tomove perpendicular to die 57 by the action of linear bearing 58 andengages therewith at a uniform depth. When a sheet 22 is placed betweenthe upper male die set 55,56 and the female die 57, actuation of forceapplicator 51 causes rib 21 to be formed between dies 55 and 57 and rib49 is formed between dies 56 and 57.

The attachment of the glass is preferably by an automatic process when arobot like device lifts glass squares from a stack and to the alreadyprepared face. The preparation is for another robot like device to cleanthe surface and to apply adhesive, preferably of the iso-cyano-acrylateinstant bonding type to the face in an appropriate pattern of dots.Because of the “instant” nature of the bonding process, long curingtimes are eliminated. The largest ring sector, complete with mirrorsweighs less than 150 KG and can be handled by a small forklift.

The preferred sequence of assembly is to complete one sector then movethe forming machine adjacent to the next sector and so continue aroundthe dish. In this way two sets of scaffolds or platforms are located atadjacent bracing plates and only one set is moved each changeover.

It will thus also be appreciated that in use in accordance with apreferred embodiment of the present invention, a method of erecting at aremote location a dish assembly 10 having a central hub 11 and an outerrim member 12, involves transporting to the remote location a pluralityof flat stacked substantially rectangular metal sheets 20 (or nestedsections formed therefrom), at the remote location forming a pluralityof arcuate structural members 13 of box-section configuration from thesubstantially rectangular metal sheets 20 or from the sections formedtherefrom, and positioning the plurality of arcuate structural members13 to extend concentrically from the central hub 11 to the outer rimmember 12. The arcuate structural members 13 abut along their inner andouter arcuate surfaces 14,15 such that load can be transferred from anouter arcuate structural member to an adjoining inner arcuate structuralmember.

A plurality of radial support arms 36 are positioned extending fromcentral hub 11 to outer rim member 12 and the radial support arms 36support the arcuate structural members 13. The substantially rectangularmetal sheets 20, or the sections formed therefrom, are formed into upperand lower channel members 18,19 which are joined to form the arcuatestructural members 13. Transverse ribs 21 are formed across channel base22 between channel flanges 23,24 within the channel by folding inwardlya portion of channel base 22, the told being deeper at one flange thanthe other such that the rib 21 formed thereby is correspondingly deeperat one flange than the other. The rib thus constitutes a cantilever andbecause the rib is formed from the channel base material, the edges ofthe substantially rectangular sheet 20 becomes angled about the rib tothereby form the arc in the arcuate member 13.

To elevate the dish assembly 10, a dish support member 32, which ismounted on rotating platform 35 on foundation 33, supports dish assembly10 within an opening in hub member 11 which is adapted to cooperate withthe dish support member 32 to elevate the dish assembly 10 with respectto the foundation 33.

The present invention in its various aspects and preferred embodimentsprovides a number of advantages over known dish assemblies where thelimited number of dishes having an area in excess of 250 sq. meters havea number of disadvantages including:—

costs which are too high for acceptable energy output costs.

aerodynamic loads which are not minimised.

actuation by means of hydraulic drives which are not optimised tominimise the onsite inventory of oil and which use complicated andcostly ram recycling techniques.

use of reinforced concrete circular tracks as foundations which isunnecessarily expensive because of the exacting levelling requirementsand the number of attachment points embedded.

To achieve the desired level of concentration, the mirrored glass inknown systems is subjected to biaxial stresses or is heatformed to dualcurvature before silvering. The mirror substrate is designed to havesufficient rigidity to span considerable distances between mountingpoints.

During installation of known dishes, large capacity cranes are requiredon site, to lift assembled or partly assembled dishes onto the base oraxis of rotation pivots. Furthermore component dimensions and form ofknown systems are not optimised to container transport.

Existing large dish assemblies have large exo-skeletal configurationswith large void, space frames or obtain their rigidity via substantialcore beam and peripheral trusses. The major components are fabricatedoff site and depending on the location of the installation, requireshipping, usually in containers. However the space frames are made fromclosed ended steel tubes of various diameters and have a poor mass tovolume ratio. Similarly trusses are mainly void and present a poor massto volume ratio. Transportation to on-site location of known systems istherefore inefficient.

The present invention in its various aspects and preferred embodimentshas a dish which is lower in cost and features the integration of themirror substrate into the structure. The major part of the dish may bemanufactured on site, reducing costs of transport. The transportedmaterials have a high mass to volume ratio. Large cylinders areopen-ended and the internal volume is accessible to accommodate smalleritems during transport.

The dish materials have corrosion resistant finish and post manufactureanti-corrosion treatment is not required. Only a brief time is requiredto assemble the dish because of the processes used. No resin castingprocesses with their associated setting and curing times are involved.Furthermore, the aerodynamic profile is enhanced because the dish stowsnearer the ground plane than other designs. The structural requirementsare therefore less demanding at the survival wind velocity.

The glass mirror panels are all the same size and remain flat and arenot subjected to stresses associated with curvature. Their size andconfiguration of the flat mirrors are well suited to robotic pick up andplace operations.

The design is flexible in that it allows high concentrations to beachieved by deforming the flat face to accept a number of smaller flatglass facets. The installation does not require large reach, highcapacity cranes for the installation and the dish is assembled on thebase.

The manufacturing plant is flexible and high cost items such as thepolygon forming mechanisms, are adjustable to cover the range of sizesrequired.

Furthermore and in general, another reason for there being a limitednumber of dishes in excess of 250 sq. meters is the weight of suchstructures when made by conventional techniques. The present inventionfacilitates the construction of large area dishes which have arelatively light weight per unit area.

It will of course be realised that whilst the above has been given byway of an illustrative example of this invention, all such and othermodifications and variations hereto, as would be apparent to personsskilled in the art, are deemed to fall within the broad scope and ambitof this invention as is herein set forth.

1. A dish assembly including: a central hub; an outer rim member, and aplurality of concentric arcuate structural members comprising at leastan inner and an outer arcuate structural members extending from thecentral hub to the outer rim member; each of the arcuate structuralmembers having an upper channel member, a lower channel member, an innerarcuate surface and an outer arcuate surface which cooperate toconstitute a box section configuration, and wherein said each upper andlower channel member comprises a channel base and a pair of channelflanges; and the inner and outer arcuate surfaces of each of the arcuatestructural members are abutted such that a gravitational or wind load istransferred from the outer arcuate structural member to the adjoininginner arcuate structural member via a fin disposed on the inner arcuatesurface of each of the arcuate structural members.
 2. The dish assemblyas claimed in claim 1, and including a plurality of radial support armsextending from the central hub to the outer rim member and adapted tosupport the ends of the arcuate structural members.
 3. The dish assemblyas claimed in claim 1, wherein the upper and lower channel members areformed from substantially rectangular metal sheeting.
 4. The dishassembly as claimed in claim 3, wherein the gauge of the metal sheetingof each inner arcuate structural member is greater the gauge of eachouter arcuate structural member.
 5. The dish assembly as claimed inclaim 4, wherein the upper and lower channel members have a transverserib formed within the upper and lower channel members across the channelbase between the channel flanges, the rib being formed from the base. 6.The dish assembly as claimed in claim 5, wherein the rib is formed byfolding inwardly a portion of the base, the inwardly folded portion ofthe base being deeper at one flange than the other such that the rib iscorrespondingly deeper at one flange than at the other flange, wherebythe rib constitutes a cantilever and whereby the edges of thesubstantially rectangular sheeting becomes angled about the rib tothereby form an arc in the arcuate member.
 7. The dish assembly asclaimed in claim 1, wherein the said channel flanges of the upper andlower channel members have outwardly and inwardly directed returns atthe respective bases thereof, such that when the upper and lower channelmembers cooperate to constitute the arcuate structural member of boxsection configuration, the returns constitute cooperating keys andrecesses respectively of adjoining concentric arcuate structural memberswhereby said wind load is transferred from the outer arcuate structuralmember to the adjoining inner arcuate structural member.
 8. The dishassembly as claimed in claim 1, and including a plurality of mirrorsaffixed to the bases of the upper channel members whereby the dishassembly constitutes a solar collector.
 9. The dish assembly as claimedin claim 8, wherein the glass mirrors are substantially square withsides substantially the width of the arcuate structural members.
 10. Thedish assembly as claimed in claim 1, and including a dish support membersupportable on a foundation and receivable within an opening in the hubmember and adapted to cooperate therewith to elevate the dish assemblywith respect to the foundation.